Since the global population structure is leading to an aging population in society, elderly people not only have to face the threats of cancer, stroke and myocardial infraction, but must also pay more attention to osteoporosis. In detail, the bone mass of the human body keeps growing after birth and reaches the maximum by age 30. After age 30, bone mass decreases every year. This especially applies to postmenopausal women, whose bone mass decreases dramatically due to the reduction of estrogen, which can induce the formation of bone mass. Moreover, in patients with osteoporosis, bones become loose and brittle, and the risk of fracture is increased. Elderly people especially may suffer fractures of the neck or thighbone by falling down, further leading to often lumbago and disability, and the bone fractures are very hard to be cured. According to statistics in Taiwan, the probability for osteoporosis fracture is about two to four times higher than the probability for stroke. The incidence of osteoporosis fracture is estimated to increase six times globally by 2050, especially in Asia. The 2009 report from the Bureau of National Health Insurance in Taiwan suggests that the incidence of osteoporosis in Taiwan among postmenopausal women is about 25% and at least 20% of men also suffer from this disease. Furthermore, the report also reveals that approximately 10˜20% of patients who experience a hip fracture will die in the first year following the fracture. This mortality rate is almost the same as with the late phase of breast cancer. In addition, 50% of osteoporosis patients cannot live independently, and 20˜25% of osteoporosis patients cannot act alone. Therefore, the health care system and society have to spend a lot of social and medical resources. Thus, this is an important research issue for the prevention and health care of osteoporosis.
In osteoporosis, the major factor causing fractures depends on the bone mineral density. Thus, the goal of treatment is to reduce bone loss or to increase bone mass and density. As of now, there are several drugs that can reduce the loss of bone mass by decreasing bone resorption, such as Calcitonin, hormone therapy and bisphosphonate. In addition, anabolic drugs, such as parathyroid hormone (PTH) can stimulate osteoblasts to increase bone formation (Riggs and Melton, 1988). Although these two kinds of drugs have been used for curing patients with osteoporosis, there still exist the following problems. First, these drugs cannot be used on people over 30 years old and those whose bone masses are reducing but do not meet the standard of osteoporosis. Second, treatments with bisphosphonate have the side effect of osteonecrosis of the jaw in patients. In order to avoid the drawbacks above, there are many nutriments for calcium supply on the market to prevent bone loss and to supply calcium nutrition in bone. However, the nutriments neither have effects on the control of bone loss, nor supply bone calcium by inefficient calcium absorption.
Recently, research on the bioactive peptides in natural products has rapidly developed. Some reports suggest that many milk-derived peptides have physiological activities, such as antihypertensive, opioid-like, immunomodulating, antithrombotic, antimicrobial and calcium-absorption enhancing properties (Zinn, 1988; Yamamoto, 1998; Shan, 2000). Thus, the researches all focus on discovering the protein from natural products that can improve osteoporosis. Furthermore, these peptides with different physiological activities in natural products do not have side effects such as those caused by chemical drugs. However, most bioactive peptides, including ACE inhibitory peptides, antimicrobial peptides and antihypertensive peptides, have to be processed into oligo-peptides by enzymatic reaction in order to have full the functions of the physiological activities (Meisel, 1999). In addition, fermented or non-fermented foods also can improve its function by proper hydrolysis (Vermeirssen et al., 2003; Hernandez-Ledesma et al., 2004).
Thus, how to obtain small-molecule peptides with physiological activities from natural products and further specifically improve the symptoms of osteoporosis are important issues in the biomedical and pharmacological fields.